Volatile organic compounds are known to pose health and environmental hazards. On the one hand, ozone depletion and global warming are now attributed to such factors as the release of copious quantities of chlorofluorocarbons (CFC's) and similar volatile compounds. On the other hand, inhalation of volatile constituents, particularly solvents or similar compounds used in a wide range of manufacturing procedures, is known to result in potentially severe health hazards. In all such cases, the characteristics which make these compositions particularly desirable in manufacturing procedures, such as the efficacy of a composition as a solvent or cleaning agent (e.g., volatility), are directly responsible for the deleterious or potentially deleterious effects accompanying their use.
Systems have been devised to minimize solvent loss during or incident to procedures in which these volatile compositions have a tendency to escape to the atmosphere. Some are recovery systems designed to retrieve the fluid and entrained materials resulting from a manufacturing procedure, such as a cleaning procedure, and thence separate the reusable fluid from contaminants. These systems tend to have common limitations or drawbacks. For example, air is often allowed to enter the system and mix with vapor, whereupon removal of the air necessarily implicates loss of volatile constituents as well. More direct sources of solvent loss may be attributed to diffusion, "dragout," and system leaks.
Indirect solvent loss, as in the case of solvent admixed with admitted air, has been addressed most commonly by means of carbon absorbers. Those recovery or control systems can become complicated and hence costly in terms of both capital investment and operating expense. Direct loss is sometimes easier to control, but many potential solutions designed for that purpose can contribute to admission of ambient air to the system, resulting in the types of problems mentioned above. Thus, it is not uncommon to find solvent systems used in, for example, the electronics industry for cleaning printed circuit boards or electronic components, to emit relatively large amounts of solvent vapor, on the order of 8 to 10 pounds of solvent per hour.
Many azeotropes of chlorofluorocarbons such as CFC-113 with alcohols or methylene chloride are known and are used for a variety of purposes. See Freon TMC, Solvent, U.S. Pat. No. 2,999,817, Freon TA Solvent, U.S. Pat. No. 2,999,815, Freon T-P 35 Solvent, U.S. Pat. No. 3,085,116, Freon TES Solvent, U.S. Pat. No. 3,905,009, Freon TMS Solvent, U.S. Pat. No. 3,960,746, and Freon T-DFC Solvent, U.S. Pat. No. 4,182,687. High boiling CFC's are in common use as cleaning solvents, usually in the form of an azeotropic mixture with an alcohol or acetone. See generally Merchant et al. U.S. Pat. Nos. 4,810,412, issued Mar. 7, 1989, U.S. Pat. No. 4,814,100, issued Mar. 21, 1989, and U.S. Pat. No. 4,812,256, issued Mar. 14, 1989, relating to use of CHF.sub.2 CHCl.sub.2.A pressurized system for recovering dissolved substances from aqueous solution using a mixture of high and low-boiling fluorocarbon solvents has also been proposed. See Knupp, Jr. U.S. Pat. No. 4,515,695, issued May 7, 1985. Henrich et al. U.S. Pat. No. 4,400,183, issued Aug. 23, 1983, describes using Cl.sub.2 CF.sub.2 as an absorption agent for noble gases, with subsequent desorption.
Many CFC's and HCFC's, such as CHClF.sub.2 (HCFC-22) have low boiling points and have accordingly been used only in applications such as aerosol propellants or refrigerants. See Ermak U.S. Pat. No. 4,510,064, issued Apr. 9, 1985, Bivens et al. U.S. Pat. No. 4,810,403, issued Mar. 7, 1989, Orfeo et al. U.S. Pat. No. 4,303,536, issued Dec. 1, 1981, Murphy U.S. Pat. No. 3,901,817, issued Aug. 26, 1975, Charle et al. U.S. Pat. No. 3,714,049 issued Jan. 30, 1973, Bargigia et al. U.S. Pat. No. 4,174,295, issued Nov. 13, 1979, and Japanese Patent Publication 5921632, published Feb. 3, 1984. Solvency, uses and other properties of CHClF.sub.2 are discussed in Sander, "Handbook of Aerosol Technology", Second Edition, Rogert E. Krieger Publishing Co., Malabar, Fla., Second Edition, 1987.
A variety of cleaning systems have been proposed which provide for recovery of solvent, e.g., by condensation of solvent vapors. See generally U.K. Patent Application 2,085,310, Apr. 28, 1982, German Patent Publication No. 3,012,759, 1981, and German Patent Publication No. 3,907,437, 1989. A closed system for cleaning articles utilizing a flushing gas circuit is described in European Patent Application No. 331,611, 1989.
Despite the availability of low-boiling halocarbons, no method or system has been proposed enabling use of such compounds in liquid form for cleaning applications in a manner similar to CFC's having higher boiling points.